Attica the Rit liquids are really easy to use and I didn't have to use vinegar to set them. There's four or five different shades of green with Rit. They don't have Flourescent colors.
The only company I've found that has florescent colors is Veniard's. It's called Fly Dye and it uses vinegar to set the color but it cost's $15 for a small jar but watched Davy McPhail on youtube and you only use a little of it. [video=youtube]
When the feather craze was going on JungleJim posted about dyeing saddles and making a bunch of $$ and he used Cushings dye, but I didn't find any flourescent colors.
Toad gave me this site for dyes, Aljo Dyes. I have to find out which type he uses from them.
http://www.aljodye.com/main.html
Led - when I tried the KoolAid, I used 2 tablespoons of vinegar and it set the color